The subject of the invention is that of a stiffener for an aircraft fuselage, its manufacturing method, as well as an aircraft fuselage equipped with such a stiffener.
The stiffeners mentioned here can be transverse stiffeners of aircraft fuselages, in particular circular frames encircling the fuselage (either in whole, either disrupted by the landing gear, for example), or beams extending at the floors, or even longitudinal stiffeners such as stringers or longerons, or even other ribs.
A conventional frame design, represented in FIG. 1, shows that the circular frame 1 can consist of an S-shaped profile, comprising a core 2, as well as two outer wings 3 and 4. The frame 1 is attached to the skin of the fuselage 5 via a stabilizer 6 and a clip 7. The stabilizer 6 and the clip 7 are attached to the fuselage 5 by attachment means 8 such as rivets, through stringers 9 which are longitudinal stiffeners. The frame 1 is attached thereto by analogous attachment means 8. The stabilizer 6 essentially comprises an oblique rib and extending in a longitudinal plane of the aircraft that is perpendicular to that of the core 2. The clip 7 comprises a wing bearing against the stringers 9 and another wing extending in parallel with the core 2, to which it is attached.
This conventional device has the drawback to be complicated, as clearly shown by FIG. 2, which illustrates an entire fuselage sector. The complexity of the assembly also generates difficulties to comply with the tolerances. The stabilizer 6 and the clip 7 are however useful to place the frame 1 at some distance from the skin of the fuselage 5 and thus increase the rigidity of the latter.
Another solution is provided in document EP-2 404 824-A, which consists of improved transverse stiffeners, having a simple structure easily integrated to the fuselage. This stiffener includes a quadrangular hollow closed trapezoidal section, consisting of a base to be attached to other portions of the fuselage, a top side opposite to the base, and two rising sides connecting the base to the top side. It has a great strength for increased stresses undergone when damage appears in the proximity thereof. Since the base can be directly attached to the fuselage via the stringers, the stabilizer and the clip become unnecessary. The rising sides and top side ensure that a sufficient quantity of matter of the stiffener is away from the fuselage skin, which maintains the rigidity of its structure.